Distribution and abundance of caddisflies (Trichoptera) in the St. Clair-Detroit River system

Abundance and distribution patterns of the caddisflies of the St. Clair-Detroit River system were investigated in 1983–84. Collections of both adults and larvae yielded 70 species representing 34 genera and 12 families. Leptoceridae and Hydroptilidae were the most common families and Ceraclea the most common genus in number of species. This study adds 21 species to the Michigan record. The hydropsychidsCheumatopsyche (81, 63, 105 m−2; log-transformed values for mean and lower and upper 95% C.L.) and Hydropsyche (70, 57, 87 m−2) were the most abundant genera collected as larvae in the St. Clair and Detroit rivers, while Oecetis (41, 35, 47 m−2) was the most abundant in Lake St. Clair. Larval densities of caddisflies in the Detroit River were about twice those in the St. Clair River, but the number of genera collected in each river was about equal (22 vs. 23). Larval abundances were higher in October than May because most genera had substantial overwinter population declines. Low densities and species richness in some areas of the St. Clair-Detroit River system may reflect in part continued water quality problems, but community structure has markedly improved and representation of pollution-sensitive organisms has increased over a 12–15 year period.